“…Cloudy skies are forecast-sensitive areas because of the large horizontal and vertical gradients in the atmospheric variables, which make the predictions under the cloudy skies very difficult (Errico et al, 2007;Geer, 2019;Geer et al, 2017Geer et al, , 2018Li et al, 2016Li et al, , 2021McNally, 2002). All-sky assimilation is expected to facilitate the forecast as clouds present because (a) mass, wind, and humidity fields can be directly improved under cloudy skies (Geer et al, 2008(Geer et al, , 2017Zhu et al, 2016), (b) observations from clouds and precipitation can provide additional information on mass, wind, and humidity (Bauer et al, 2006;Chen et al, 2020;Li et al, 2020;Sawada et al, 2020), and (c) better hydrometeor initialization can be obtained (Chen et al, 2015(Chen et al, , 2016Jones et al, 2013;Jones & Stensrud, 2015;Wu et al, 2016;Wu & Zupanski, 2017). Therefore, some numerical prediction centers (NWP) have operationalized the all-sky assimilation of satellite observation, such as the European Center for Medium-range Weather Forecasts (Bauer et al, 2010), the NOAA National Centers for Environmental Prediction (Zhu et al, 2016), and Met Office (Carminati & Migliorini, 2021), while others are ongoing to develop corresponding all-sky assimilation techniques, such as Japan Meteorological Agency (Okamoto et al, 2019), Météo-France (Duruisseau et al, 2019), and the German Weather Service (Harnisch et al, 2016).…”